Case Studies, Crushing, Mobile Plant, Processing, Sand Processing, Screens & Feeders

All-in-one washing plant advances case for manufactured sand

As manufactured sand grows on the Australian quarrying industry, so does demand for a plant specifically tailored to this application. Damian Christie spoke to Daniel Webber about how modular equipment is providing wet processing options for the driest of quarries.

The use of natural sand in construction materials applications around the world is becoming increasingly restricted. Obtaining approvals for sand quarries in Australia is becoming increasingly more difficult, due to bureaucratic concerns about the impact of extraction and processing on the environment.

There is also a scarceness of sand reserves in some parts of Australia, most especially around the Sydney Basin, making sand products more expensive if they are transported from hundreds of kilometres away.

Water management – especially in sand applications, at a time of heavy drought – is extremely expensive for quarrying operations. Not only are slime ponds costly to maintain (and frowned upon by some regulatory bodies) but there is the extra expense of rehabilitation once the site is depleted.

As a result, the quarrying industry has for several decades explored the replacement of natural sand with manufactured sand.

In the NSW southern tablelands region, Boral Peppertree Quarry has been developing manufactured sand from crushed stone as value add, especially as there is still a strong demand for sand in the Sydney market. In Victoria, Alex Fraser Group, a subsidiary of Hanson Construction Materials, has made significant investments for more than a decade in recycled aggregates technology, developing manufactured sand fines from both recycled concrete and road base materials, and more recently recycled glass. The end products have been successfully employed in road base and concrete applications.

Cement Concrete & Aggregates Australia (CCAA) has also previously published a research paper on the national test methods and specifications of manufactured sand, based on input provided by a working party of representatives from Boral, Hanson, Holcim and Barro, and the CCAA. (1)

Daniel Webber, CDE’s regional manager for Australasia, told Quarry this report was an example of the “great work” competitive stakeholders do when they pool resources. He said the report helped to “debunk myths about manufactured sand and concrete products”.

The CCAA report also clarified the dual challenges of sand washing plants in developing manufactured sands from crushed rock. “Washing is trying to do two things: reduce the fines content to specified levels, and then eliminate the clays and silts that come into the sand fraction,” Webber explained.

“The clays and silts reduce the strength of the concrete and too much fine rock increases water absorption, so there is a trade-off for concrete manufacturers when they do their batching, with cement/water ratios.

If there is too much fine material, more water and cement will need to be added to balance out the mix, so it raises production costs.

“It’s a two-fold problem, and it’s a case of working with concrete manufacturers to get the blending targets right. What we find is that some of the manufactured sands available on the market are simply unwashed crusher fines, which produce uneven results and can significantly reduce the quality of applications such as concrete sands.

“With cyclone-based washing, crusher fines are turned into high value manufactured sands, proven to be superior in quality to washed natural sands, hitting the specification target in one go and reducing manufacturers’ overall operational costs.”

CDE has also undertaken its own exhaustive research into manufactured sand for its various divisions, eg Primo (sand and aggregates), Reco (construction and demolition waste recycling), Solv (industrial sands) and Meta (mining) (2). The company’s focus has been on maximising sand and aggregate resources to create high value materials for a variety of applications, encouraging the circular economy model.

“CDE has taken the lead to prove that manufactured sand can be – and is – as reliable as natural sand products,” Webber said. “Some hard rock resources lend themselves more readily to manufactured sand applications than others; it’s about creating an understanding of the complexity of the process and bringing efficient solutions to operators.

“Notably, each M-Sand has different qualities depending on the original crushed rock it was created from. For example, M-Sand produced from granite rock helps concrete structures to withstand extreme environmental conditions and prevents corrosion of reinforcement steel. Size and shape also play an important role in the workability of concrete.

“With more sand surface area, there is an increased need for cement and water to bond the sand with coarse aggregates. Using CDE M-Sand with less surface area means the concrete can be equally as workable using less water, and consequently less cement. As cement is the most expensive ingredient of concrete mix, representing around 50 to 60 per cent of the cost at less than 20 per cent of the volume, this further emphasises why the consistency of clean, in-specification CDE M-Sands is so important to achieve high strength concrete.”

Webber continued: “The adoption rate of CDE M-Sands technology is growing at a fast pace across the world. For instance, in India, we sell one Combo plant for use by manufactured sand operators every week.

“Manufactured sand complements quarrying businesses. These companies produce aggregates for their greater markets, and by doing so they produce dust, so why not upgrade that dust into a higher end, sellable product? We know of the pressures on different markets to find innovative alternatives to natural reserves, as we’ve seen with the depletion of natural resources around Sydney and Melbourne.

“Rather than looking for natural sand resources further afield, wouldn’t hard rock deposits closer to the cities become more viable as sources of high value construction sand?”

Washing in dry places 

The challenge for CDE in Australia has been to introduce wet processing systems to hard rock quarrying operations that so far have not considered washing their products.

“When we started,” Webber said, “hard rock quarry operators generally had been running quarries for decades and were very good at crushing and screening. However, the sites weren’t set up for washing. Often, they didn’t have electrical power supplies nor a sophisticated water circuit on site.”

To address the needs of customers in Australia – and indeed around the world – who required efficient alternatives to the depletion of natural resources to ensure the sustainability of their businesses, CDE’s award-winning Research & Development team developed the Combo all-in-one plant.

The Combo features patented technology that combines feeding, sizing, sand washing, stockpiling and waste water management on one compact chassis; it allows to run the full feed to the final product process at one touch of a button, with up to two in-spec final materials being produced simultaneously, ready for market straight from the belts.

Each Combo modular plant is bespoke to the client’s needs, with a range of options that allows for tonnage flexibility to suit all sizes of operations – and anticipates future needs – from 70 to 500 tonnes per hour.

Webber added: “The Combo is a plug-and- play system that allows for unrivalled control of silt cut points thanks to a highly efficient cyclone-based process; the system also prevents loss of sand in the overflow and loss of valuable fines to ponds. Every grain of valuable product is retained in the system.

“All processing stages of the Combo plant have been conceived with low energy consumption as a must, whilst operators also benefit from exceptionally economical water consumption, with an incorporated water management unit that recycles up to 90 per cent of used water directly into the system. With all modules working as a closed circuit, materials production is seamless, efficient and in specification every time.

“As valuable fines lost to ponds is a thing of the past, operators can reduce the footprint of their ponds, save on maintenance and therefore on downtime, speeding up production times and return on investment.

“In Australia, the Combo is our response to maximising production on hard rock sites not being set up for washing. Again, it’s a small footprint because often in a hard rock quarry, you have equipment moving around regularly on a hard rock basis.”

The Combo is available worldwide in five models corresponding to various capacities. Each variation of the washing and water recycling plant is equipped with cyclones (starting at 500mm diameters, with multiple and bespoke sizes on later models), dewatering screens (multiple screens on the 900 and 1500), an AquaCycle thickener (built to CDE’s standard sizes) and a Poly Plant.

Compact footprint

Webber said the Combo series is a perfect fit for the processing of manufactured sand. “The feed to a manufactured sand plant is often more consistent because it’s coming off a crusher circuit, so you’re not getting many oversized fractions or variable feed,” he said.

“That stability means we have a much smaller footprint and potentially there is no need for a pre-screen. The on-board process water systems – the thickener and floc station – are incorporated in the single chassis. A Combo can be commissioned in about five days, so it’s readily deployable and easily relocatable to another site. Often these hard rock quarries use contract mining operations, so again this piece of equipment suits that business model.

“The compact footprint means we’re doing less pumping than a traditional plant, and slurry pumps are a big source of power draw,” Webber said of the Combo’s energy efficiency features. “Our thickeners are all very efficient and the Infinity screening technology is one

of the most energy-efficient on the market. So CDE offers an efficient response to water and energy consumption.

“When producing manufactured sand, CDE’s wet processing equipment achieves high recovery of water from the sand before stockpiling, so the finished product contains as little as 12 to 15 per cent moisture. The slimes are pumped away, or we can use a filter press to raise the water recovery rate to up to 95 per cent.”

The Infinity dewatering screen operates in a dual pass capacity that delivers fine, coarse or “all-in” sands.

Not only does the Combo already comply with Australian industry standards, but it can be customised to suit a producer’s specifications and be set up alongside another washing plant, where applicable. “The Combo is just another part of CDE’s modular range,” Webber said. “We have already created combinations that include log washers for instance. CDE solutions can be customised

to the exact requirement of operators. We’re not trying to make stock equipment the customer’s problem, we’re responding to their process problems.”

Solo or tandem?

The Combo was launched at bauma, Germany, in April 2019 and is still to become a mainstay of the Australian sand processing market, but CDE is far from being new on the market. The company has enjoyed success with its EvoWash modular plant, which has more than 40 installations across Australia.

Like the Combo, the EvoWash – available in four models – is equipped with Infinity screening technology, cyclones arrangements which can be tailored to the customer’s requirements and Warman pumps. As a modular plant, it can be assembled after transportation in 12m (40’) containers.

The EvoWash can also assist with the manufactured sand process in a standalone capacity.

Webber said the EvoWash can also assist with the manufactured sand process in a standalone capacity if a site has tailings facilities and doesn’t require a thickener. “The size range that the EvoWash operates in – with capacities of up to 250 tonnes per hour – means it is suitable for any size of operation,” he said.

“We have seen clients transferring material directly from the wash deck of their crusher plant into the sump of an EvoWash, so it can be ‘plugged and played’ for a relatively small investment.”

He said the EvoWash could operate with non-CDE types of sand washing plant. “That’s one of the first discussions we have with a client – does it make business sense to complement the existing equipment or is there a business case to replace all of the equipment with an EvoWash? That’s always going to come back to a commercial discussion, and we let the client drive that.

“Obviously, there are synergies when the EvoWash is installed with another CDE plant, from a process control and interface point of view. However, it can be standalone equipment in a brownfield application.”

Webber said the reception from the domestic market to the EvoWash boded well for the Combo. “We have an EvoWash plant now at its third home in Australia,” he said. “It has moved from Western Australia to the Northern Territory to Melbourne, and that tells you the value that the owner sees in the equipment. It’s well built, it’s built to last, and it’s a robust piece of equipment, so we’re extremely proud of that.

“We’re equally confident about the Combo, which is built on the same principles as the EvoWash.”

Webber said CDE’s CustomCare programme – which comprises after sales and support, parts, preventative maintenance, asset care and the suite of CDE CORE smart technology tools – would assist with maintaining the wear and service life of the EvoWash and the Combo, even when dealing with abrasive materials.

“Angular sands or manufactured sands are more aggressive than rounded, alluvial sands but CDE offers a comprehensive, after sales service that guarantees the smooth running of the plant over its lifetime.”

For hard rock producers investigating manufactured sand as added value to their operations, this assurance will certainly be very welcome news, indeed.

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